This study is a single-center, single-arm, prospective clinical trial designed to evaluate the efficacy of local excision followed by postoperative chemoradiotherapy in patients with early-stage low/ultra-low rectal cancer. The study plans to enroll 60 patients with T1-2N0M0 low/ultra-low rectal cancer.

Baseline examnation: All enrolled patients in this study, in addition to routine laboratory and imaging examinations such as blood routine, blood biochemistry, serum tumor markers (Incl. CEA, CA-199, CA-724 β2-microglobulin, Ferroprotein), chest CT, abdominal and pelvic MRI, etc., were required to undergo KRAS, NRAS, BREF, PD-L1, MMR/MSS testings before surgery, and blood lymphocyte subgroups were analyzed before surgery.

All enrolled patients will first undergo local tumor resection. Adjuvant therapy will be initiated 4-6 weeks postoperatively based on pathological staging:

For pT1N0M0 patients without high-risk features:

Active surveillance OR Radiotherapy alone (Prescription: Pelvic field irradiation 45Gy in 25 fractions)

For pT2N0M0 or pT1N0M0 patients with adverse prognostic factors (including poorly differentiated histology, lymphovascular invasion, positive margins*, tumor infiltration beyond the outer third of the submucosal muscle layer（SM3 level）, or submucosal invasion >1mm):

Adjuvant chemoradiotherapy (Prescription:Pelvic field irradiation 45Gy in 25 fractions PLUS Local tumor bed boost 5.4Gy in 3 fractions；Concurrent chemotherapy: Oral capecitabine 825mg/m² twice daily)；For patients with positive margins after local excision: Re-excision followed by adjuvant chemoradiotherapy OR Dose-escalated chemoradiotherapy (Prescription: Pelvic field irradiation 45Gy in 25 fractions PLUS Local tumor bed boost 14.4Gy in 8 fractions)；

For patients with staging > pT2N0M0:

Total mesorectal excision (TME) Following treatment completion, patients will enter clinical follow-up surveillance.

Inclusion Criteria:

1. Age ≥18 years, regardless of gender
2. ECOG performance status 0-1
3. Biopsy-proven rectal adenocarcinoma
4. Distal margin of primary tumor ≤8 cm from anal verge
5. Clinical stage I (cT1-2N0M0)
6. Strong organ preservation preference with refusal to undergo abdominoperineal resection (Miles operation)
7. The surgeon determined a local resection was feasible
8. No contraindications to chemoradiotherapy

Exclusion Criteria:

1. Failure to meet the above inclusion criteria
2. Patients refusing to sign informed consent
3. Impaired cognitive function or psychiatric disorders
4. Patients deemed ineligible by investigators